Factfile: the Moon

By Conor McKeever

First published 4 April 2016

The surface of the Moon is speckled with cavernous valleys and deep craters. So why doesn't Earth have a similarly scarred surface?

With one side forever facing us, and with too little atmosphere to allow storms or clouds to form, the Moon appears to be a calm, unchanging world. But look a little closer and there is evidence of a much more violent history.

When our solar system was still forming, collisions between planets, moons, asteroids and comets were more common than they are now. Impact craters, formed when asteroids and comets strike a larger body, litter the Moon's surface.

The largest, the South Pole-Aitken Basin on the moon's far side, is 2,500 kilometres wide and 13 kilometres deep - big enough to stretch from London to Moscow and swallow one and a half Mount Everests.

In fact, it's so vast that many other craters have formed within it, such as the Antoniadi Crater - visible in this image, one of 77 composite photographs appearing in Otherworlds: Visions of our Solar System.

Permanent scars

The Moon's speckled surface has been caused by meteor bombardment over 4.5 billion years.

Earth went through a similar barrage of space debris in the early part of its history, but geological processes have scrubbed evidence of the craters away.

Any craters that were formed thousands of years ago have been eroded by our planet's weather systems, filled in with lava, or hidden as the crust gets recycled.

The Moon has no atmosphere, tectonic movements, active volcanoes, weather systems or wind to erase its blemishes, so any mark that is made on its surface will stay there permanently - even astronauts' footprints.

Audio commentary extract

How do we work out what moon rock samples are made of? In this extract, Dr Joe Michalski talks to Dr Stanislav Strekopytov, a Senior Analytical Chemist at the Museum, about his work analysing moon rocks brought back by the Apollo astronauts.